music_library/backlog/completed/ml-25 - recompact_positions-issues-per-row-UPDATEs-instead-of-bulk.md

id, title, status, assignee, created_date, labels, dependencies, references, priority

id	title	status	assignee	created_date	labels	dependencies	references	priority
ML-25	recompact_positions issues per-row UPDATEs instead of bulk	Done		2026-04-20 08:51			https://github.com/cloud8421/music_library/issues/154	medium

Description

GitHub: created 2026-04-05 · updated 2026-04-06 · closed 2026-04-06

Summary

RecordSets.recompact_positions/1 fetches all items into memory and issues individual UPDATE queries for each item whose position changed. The same module already demonstrates a bulk UPDATE pattern in reorder_records_in_set/2.

Why This Matters

• For a record set with N items, this can issue up to N individual UPDATE queries
• The same module's reorder_records_in_set/2 (lines 142-157) uses a single bulk UPDATE with CASE expressions — proving the better pattern is already known

Affected Files

• lib/music_library/record_sets.ex (lines 239-254)

Suggested Fix

Rewrite recompact_positions/1 to use a single UPDATE ... CASE statement, consistent with reorder_records_in_set/2.

Acceptance Criteria

• Position recompaction uses a single bulk UPDATE
• Positions are correctly reassigned with no gaps
• No regression in ordering behaviour

• #1 Position recompaction uses a single bulk UPDATE
• #2 Positions are correctly reassigned with no gaps
• #3 No regression in ordering behaviour